Scroll compressors having a fixed scroll and a movable scroll with spirally-arranged wraps engaged with each other have been known (see, e.g., Japanese Unexamined Patent Publication No. 2012-117519). A housing is disposed on the back surface of the movable scroll, and an Oldham coupling, which prevents the movable scroll from rotating on its own axis, is disposed between the end plate of the movable scroll and the housing. In this scroll compressor, a low-pressure gas is taken in and compressed, while a compression chamber formed between the wrap of the fixed scroll and the wrap of the movable scroll expands and shrinks during revolutions of the movable scroll.
A seal ring, which is fitted in a seal groove formed in the top surface of the housing, is provided on the back surface side of the movable scroll. A high-pressure fluid in the middle of compression is introduced into a space surrounded by the seal ring, and this causes the end plate of the movable scroll to be pushed against, and hence in pressure contact with, the end plate of the fixed scroll. As a result, the compression chamber is closed and prevents a working fluid, such as a refrigerant, from leaking from the compression chamber.